Compensating device for compasses



March 19,1935. w. E. HULL COMPENSATINGv DEVICE FOR COMPASSES Filed Maron 23. 1934 Patented Mar. 19, 1935 Application March 23,

2 Claims.

My invention relates to compensating devices for ccmpasses, particularly Compasses for use on automobiles, boats and aircraft, where the earths magnetic field is distorted by magnetism Yfrom local metal and electrical equipment.

lvost compensating devices now in use employ two magnetic elements which act at right angles to each other. Each' of these elements is either so constructed that its effective strength may be varied or is made up of a plurality of small magnets and its strength varied by adding or removing magnets. Such devices are dilicult to adjust, requiring the services oi skilled workmen who understand the principles involved.

An object of my invention is to provide an effective compensating device which, by following denite rules, can adjusted by one who is not familiar with the laws of magnetism and the principles involved in compensating compasses. Other objects are to provide a device of simple construction which will be neat in appearance and economical to manufacture.

Referring to the drawing, Figure l shows a side view of the compensating device mounted under a magnetic compass.

Figure 2 shows a front view or" the device mounted under the compass.

Figure 3 shows a pian view or the compensating device, taken on the linel 3 3 oiFigure 1.

Figure e shows a section through the compensating device, taken on the line .4 4 of Figure 3.

Figure 5 shows a section through the device, taken on the line 5 5 of Figure 3. y

lThe form oi my invention shown on the drav ing is adapted to be used with'a magnetic oom-v pass l0, which is equipped with a rubber vacuum cup l1, for securing the compass to an approximately vertical surface such as the dash or windshield of an automobile 12. l

The important features of this device are the dial 13, which is graduated to correspond'to the markings on a compass card, and the permanent magnet 14. The magnet le, lies in an approximately horizontal piane and is rotatable about an approximately vertical axis. The distance between the magnet 1li, and the compass 10, is varied to vary the strength or" the induced magrnetic eld in the vicinityof the compass.

0 The dial 13, is oi any suitable non-"nagnetic material such as phenolic resinous material. It has a. cylindrical portion extending downwardly, through which there is a hole to take the per- 55 manent magnet 14. A -suitable non-magnetic casing 15, may be provided with a cavity to take 'oorfircivss'rmo'nnvioaron'ooMrassns Waiter ganan, Warren, ohio; V

'1934; Serial No 717,011, p @in azsj cured in place without the compensating device. Y Y

If it does not indicateL the true direction the automobile is gradually turned around until the compass does indicate the true direction. VThereY will be one direction of travel in which the compass does indicate correctly. This compass reading is noted and the dial 13, on the compensating device, isset to correspond to this compass reading. The Vautomobile is now` headed in a known direction, approximately at" right angles tothe direction, in which the com- 2.0*

pass reads correctly Without the compensating device. The compensating device is now seit* cured in place, just close enough to bring the compass card to a correct reading. The compass will now read accurately for each direction of travel.Y In explaining the principle of this -device1 will irst consider a compass mounted on the windshield of an automobile with no compensating device.

range themselves parallel with the magnetic field in thevicinity of the compass. 1 will consider this magnetic eld as being made up of two component forces. One component is the earths Y magnetic'force and the other is the resultant of 35 'Y the forcesV due to local influences. The latter component remains at a xed angle relative to the longitudinal axis ofithe automobile, regard'- less of the direction the automobile is headed.

When the automobile is headed in suchY a direc- 40V tion that the compass gives a true reading,rthe' two component forces are parallel with each other, therefore this compass reading determines the angle between ther longitudinal axis of the automobile and the resultant ofthe Aforces'due 4s Y The compass magnets will arplaced at such a distance from the compass that the induced force is equal to the resultant of the forces due to local influences, the compass will indicate accurately for all directions of travel as it would if there were no local iniluences present.

The surface on which the compass and compensating device is mounted need not be absolutely vertical. They will operate on a surface such as a sloping windshield.

While the drawing, illustrates one practical form of my invention, I do not Wish to be limited to the construction shown as it is obvious that various changes could be Vmade without departing from the essentials of theinvention.

I claim: j

1. A compensating device for'compasses com- Y the compass. If the compensating device is now downwardly, a permanent magnet, there being a hole diametrically through said cylindrical p01'- tion to take said permanent magnet, a casing having a cavity to take said cylindrical portion, a screw extending through the Vbottom of said casing and engaging said portion and an elastic vacuum cup secured to said casing.

2. A compensating device for compasses comprising a dial having compass card graduations, said dial having a cylindrical portion extending downwardly, a permanent magnet, there being a diametrical hole through said cylindrical portion to take said magnet, a casing having a cavity to take said cylindrical portion, an indieating mark on said casing for co-operation with said graduations and means for supporting said casing.

prising a dial having, compass card graduations,

said dial having a cylindrical portion extending WALTER E. HULL. 

